Assignment 03 Frequency vs Direction

This assignment is meant to help explore a some of the physical aspects of sound propagation in an echoic environment which dramatically affect recording quality.

Specifically we will focus on how frequency relates to directionality of sounds and how position in the room may alter the balance of timbres in a recording.

Tools needed:
Means to play test signals in a room at levels between 60 and 90 dB SPL, while being able to move/rotate the loudspeaker.
An SPL meter or SPL metering app for your mobile computing device.
Ear plugs (your ears are not needed as much for this experiment).
Test signal specifics:
All test signals should be generated at -20dB inside the software
Sine waves of variable frequencies
Pink noise waves o
filtered pink noise which passes only frequencies below 250 Hz
White noise waves of variable duration
Filtered white noise with passes only frequencies above 2000 Hz
Play a 1kHz sine wave through your loudspeakers such that you get an SPL meter reading in the 65-75 dB SPL range when 1 meter (~3 feet) from the loudspeaker.    Once you have established that you have control of the sound system and SPL meter, you may begin the experiments.  Do not exceed SPL levels above 85 dB SPL, especially with the filtered white noise.


Measure 5 or more non-harmonically related sine waves (spread between 100 Hz and 8kHz) and the 4 noise signals at several increments, rotating the loudspeaker in place in 15º or 30º for example.  Take no more than 10 seconds per measurement.

Repeat the above for the 4 noise signals, but this time rotate the SPL meter instead.

Using only the unfiltered noise signals,  measure the levels of the signals at 0.5 meters, 1 meter, 2 meters and if space allows, 4 meters.

Plot the results of your experiments
Analyze and discuss these results, especially think about your results in the context of the reading.
From these measurements, how might you expect recordings to differ with distance and orientation of the microphone?
How might you quickly test your expectations using your voice and a mobile computing device?

Report due as blog post before our next meeting.
Use comment field below to link your report.


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